[PATCH] bdi: Increase the concurrecy level of cgwb_release_wq

Tejun Heo
2018-05-23T23:25:14Z

cgwb_release_wq was added to isolate and limit the concurrency level
of cgwb release work items. The max concurrency was set to 1 per CPU
but we do want some level of concurrency as otherwise it ends up
calling, through bdi_unregister(), synchronize_sched_expedited()
back-to-back for each release work item.

Let's allow them to bunch up a bit.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Rik van Riel <riel@surriel.com>
---
mm/backing-dev.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 8fe3ebd..f9a2268 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -790,9 +790,10 @@ static int __init cgwb_init(void)
/*
* There can be many concurrent release work items overwhelming
* system_wq. Put them in a separate wq and limit concurrency.
- * There's no point in executing many of these in parallel.
+ * Allow some level of concurrency so that we can batch on
+ * synchronize_rcu_expedited() calls in bdi_unregister().
*/
- cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
+ cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 16);
if (!cgwb_release_wq)
return -ENOMEM;